Project Summary/Abstract Osteoporosis and low bone mass (osteopenia) are estimated to affect 55 percent of the American population over the age of 50; over 50 million people in total, with major consequences for the patients' quality of life. The current standard treatment for osteoporosis is administration of nitrogen-containing bisphosphonates (NBPs). However, the mechanism by which these highly-charged drugs enter, traffic through, and reach their molecular targets and effect target cells is poorly understood. The long-term goal of this proposal is to deconstruct the molecular pathways essential for NBP response. To do this, I will build upon preliminary genetic studies by using cell assays and mouse models, as well as in vitro binding and functional assays to explore the interactions between NBPs and my identified targets. Our previous work utilized two distinct high-throughput genome-wide screens to identify over 200 genes required for the action of NBPs. In two recent manuscripts, I have initially focused on the role of two genes, ATRAID and SLC37A3, that strongly affect the response to NBPs, and found them likely to be required for the endocytic trafficking of these drugs. This proposal builds upon this preliminary work to i) characterize the physiological role of ATRAID and SLC37A3 in the organismal response to NBPs, ii) further examine their basal molecular function and how they facilitate NBP trafficking, and iii) investigate the role of two transcription factors, associated by GWAS with changes in BMD, that when depleted may sensitize cells to the effects of NBPs. Together, these studies generate a broader picture of the molecular pathways that NBP uses to affect cells by investigating other genes identified in our initial screens. While this proposal by necessity focuses on a subset of identified genes, I envision it will set the stage for my future work determining how genes identified in our screens may predict patient response to NBPs, including efficacy of treatment, dosage of NBPs needed, and adverse side effects. Moreover, this focus on understanding the mechanisms of an inexpensive, commonly prescribed drug will bring new perspectives and hypotheses to the development of treatment strategies for osteoporosis. During the early stage of this award, I will gain valuable technical skills, including in analysis of mouse models of osteoporosis, culture of primary bone cells, and biochemistry of protein interactions, as well as a deeper training and immersion in bone and endocrine biology, that will altogether enable me to develop a unique research program, which I intend to establish at a hospital-based research institute. Under the mentoring of my formal advisory committee, I will develop important soft skills, such as presentation skills, lab leadership, and grant writing. This combination of training, support and career mentoring will be instrumental in my transition to independence as a tenure-track faculty member.